Lighting systems for inspecting glassware are well known in the art. For example, U.S. Pat. No. 4,682,023 by Yoshida, issued July 21, 1987, describes a system for detecting defects in the mouths of bottles. In one embodiment, this system comprises a light source followed by a diffuser and a mask placed below the bottle to be inspected and an additional mask and a photoelectric sensor placed above the bottle. The light enters the bottle from its bottom, passes through the inside of the sidewall of the bottle, travels upward within the sidewall and is then emitted from the mouth to be detected by the photoelectric sensor. An electric processor determines whether there are areas in which the light has been blocked, which is indicative of a defect.
One disadvantage of the system disclosed in the Yoshida patent is that it is only capable of detecting defects which inhibit the transmission of light upward through the sidewall of a bottle. Therefore, defects located outside of, but adjacent to the sidewall of a bottle often cannot be detected using this system. Another disadvantage is that if it is desired to inspect both the mouth and the bottom of the bottle, then a beam splitter, two separate masks and two separate photoelectric sensors must be employed, as illustrated in FIG. 7 of the Yoshida patent.
A system which is capable of detecting both opaque and transparent defects in bottles is disclosed in U.S. Pat. No. 4,547,067 by Watanabe, issued Oct. 15, 1985. Watanabe discloses a system that can be employed to inspect either the sidewall of a bottle or the bottom of a bottle. However, there is no disclosure of inspecting both areas simultaneously. Another disadvantage with the system disclosed in the Watanabe patent is that it is relatively complex The system requires the use of a polarizer and a quarter wave plate placed between the light source and the bottle and an additional polarizer and quarter wave plate placed between the bottle and the radiation detection means.
Yet another system is disclosed in U.S. Pat. No. 4,610,542 by Ringlien, issued Sept. 9, 1986. This patent employs generally horizontal collimated light having a vertical gradient of brightness produced by placing a showcase light behind the upper area of a diffuser plate. The light passes through a first lens, a bottle to be inspected, a second lens, and finally illuminates a radiation detection means comprising a vertical array of pixels. Refractive defects change the intensity of the radiation that strikes the pixels and, therefore, this system can detect transparent refractive defects in the sidewalls of bottles. There is no disclosure, however, of detecting defects in the bottoms of bottles.
One defect commonly encountered in glassware is what is referred to as "stuck glass". During the manufacture of glassware, such as bottles, a newly formed, hot bottle will occasionally shatter. Some of the resulting pieces of glass will land inside adjacent bottles, entering through the mouth and sticking to the bottoms or the lower portion of the sidewalls of the bottles. Because the mouths of most bottles are typically relatively small, the vast majority of the stuck glass found inside bottles will be on the bottom or the lower half of the sidewalls of the bottle. Stuck glass on the inside of bottles can be dangerous because, if food or beverage products are placed in the bottle, the stuck glass may eventually break off and be consumed, causing injury to the consumer.
Therefore, it would be advantageous to provide an inspection system which can detect transparent defects, such as stuck glass, in transparent objects, such as bottles and jars. It would also be advantageous to provide an inspection system that can simultaneously inspect the bottom and the lower sidewall portions of jars and bottles. Furthermore, it would be advantageous to provide an inspection system which can discriminate between undesirable defects, such as stuck glass, which possess sharp edges having small radii of curvature, from desirable markings, such as a mold marking, which have larger radii of curvature.